My version of sombody else’s code: Finding the Index of an item in a Drag Drop operation

While working on an application that requires drag and drop, I ran into trouble when trying to figure out where in the target list (in my case, a ListBox) to insert the dropped item. I ran across Josh Smith’s article Drag and Drop Items in a WPF ListView which covers (quite nicely) how to handle drag and drop operations within and between ListViews.  While reading through the code, I found that he uses some code from Dan Crevier which was posted on Lester’s Blog. Ok, now that I have taken you through the tangled web of other people’s code, I will share how I used the code and changed it a little to work in my situation.

 

        public static Point GetMousePosition(Visual relativeTo)
        {
            Win32Point mouse = new Win32Point();
            GetCursorPos(ref mouse);

            System.Windows.Interop.HwndSource presentationSource =
                (System.Windows.Interop.HwndSource)PresentationSource.FromVisual(relativeTo);

            ScreenToClient(presentationSource.Handle, ref mouse);

            GeneralTransform transform = relativeTo.TransformToAncestor(presentationSource.RootVisual);

            Point offset = transform.Transform(new Point(0, 0));

            return new Point(mouse.X - offset.X, mouse.Y - offset.Y);
        }

        public static int GetIndexUnderDragCursor(ItemsControl control)
        {
            int index = -1;
            for (int i = 0; i < control.Items.Count; ++i)
            {
                if (control.ItemContainerGenerator.Status == GeneratorStatus.ContainersGenerated)
                {
                    DependencyObject item = control.ItemContainerGenerator.ContainerFromIndex(i);
                    if (IsMouseOver(item as Visual))
                    {
                        index = i;
                        break;
                    }
                }
            }
            return index;
        }

        public static bool IsMouseOver(Visual target)
        {
            if (target == null)
                return false;
            Rect bounds = VisualTreeHelper.GetDescendantBounds(target);
            Point mousePos = GetMousePosition(target);
            return bounds.Contains(mousePos);
        }

I didn’t change the GetMousePosition method at all from what I found on Lester’s blog.  Then I slightly modified some of Josh’s code so that it is a little more general.  I hope this helps.  Suggestions welcome.

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